There have been conventionally known compressors which are provided with a bypass passage allowing communication between a compression chamber and a suction side of the compressor and whose volume is controlled by partially returning refrigerant in the compression chamber through the bypass passage to the suction side.
For example, for a compressor disclosed in Japanese Unexamined Patent Application Publication No. 59-12264, a bypass passage passes through the sidewall of a cylinder, and an upstream end of the bypass passage is opened in the inner circumferential surface of the cylinder. When the bypass passage is closed by an opening/closing mechanism placed somewhere along the bypass passage, this closing allows compression of the entire refrigerant sucked into a compression mechanism, resulting in discharge of the compressed refrigerant. On the other hand, when the bypass passage is opened by the opening/closing mechanism, the refrigerant sucked into the compression chamber partially flows out into the bypass passage, and only the remaining part of the refrigerant is compressed, resulting in discharge of the compressed refrigerant.